Boosting Hydrogen Evolution at Visible Light Wavelengths by Using a Photocathode with Modal Strong Coupling between Plasmons and a Fabry‐Pérot Nanocavity

Hot‐hole injection from plasmonic metal nanoparticles to the valence band of p‐type semiconductors and reduction by hot electrons should be improved for efficient and tuneable reduction to obtain beneficial chemical compounds. We employed the concept of modal strong coupling between plasmons and a Fabry‐Pérot (FP) nanocavity to enhance the hot‐hole injection efficiency. We fabricated a photocathode composed of gold nanoparticles (Au−NPs), p‐type nickel oxide (NiO), and a platinum film (Pt film) (ANP). The ANP structure absorbs visible light over a broad wavelength range from 500 nm to 850 nm via hybrid modes based on the modal strong coupling between the plasmons of Au−NPs and the FP nanocavity of NiO on a Pt film. All wavelength regions of the hybrid modes of the modal strong coupling system promoted hot‐hole injection from the Au−NPs to NiO and proton/water reduction by hot electrons. The incident photon‐to‐current efficiency based on H(2) evolution through water/proton reduction by hot electrons reached 0.2 % at 650 nm and 0.04 % at 800 nm.